The production of DAC by oxidative direct carbonylation of aromatic hydroxy compounds in the presence of CO, O2 and of a precious metal catalyst is known (see, for example, DE-OS 27 38 437, U.S. Pat. Nos. 4,349,485, 5,231,210, EP-A 667 336, EP-A 858 991, U.S. Pat. No. 5,760,272). The precious metal used is preferably palladium. In addition, a co-catalyst (for example, manganese salts or cobalt salts), a base, sources of bromide, quaternary salts, various quinones or hydroquinones and drying agents may be used. The reaction may be carried out in a solvent.
However, the known processes do not deliver adequate yields for a technical conversion and produce relatively large quantities of secondary products. It is therefore desirable to provide a process which is optimised with regard to yield and quality of product.
A process has now been found which renders possible a surprising increase in the selectivity of the reaction, i.e. the decrease of secondary products with constant product yield.